Method of producing pure alumina



Nov. 19, 1935.

W. FULDA ET AL METHOD OF PRODUCING PURE ALUMINA Filed June 1, 1934 Ga/c/nea clay Pure Al 0 0g.

@MM MM W0 Mag 9% P0227, PM 9" Patented Nov. 19, 1935 I UNITED STATES PATENT OFFICE METHOD OF PRODUCING PURE ALUMINA Wilhelm Fulda, Lautawerk, Erich Wiedbrauck, Essen, and Rudolf Reinhard Bruno Wittig, Lautawerk, Germany, assignors to the firms Vereinigte Aluminium-Werke Aktiengesellschaft, Lautawerk (Lausitz) Germany, and Th. Goldschmidt A.-G., Essen (Ruhr), Germany Application June 1, 1934, Serial No. 728,622 In Germany June 8, 1933 8 Claims. (01. 23-443) This invention relates toamethod of producing reason of the described combination it is ac pure alumina. complished that for the production of the alumina In the treatment of clay and similar minerals there may be employed the cheapest raw matewith the assistance of acids for the production rial (clay) and the cheapest disintegrating agent of alumina it has heretofore usually been over- ($02), and notwithstanding the alumina possesses 5 looked that the clays contain a number of slight the highest degree of purity, i. e., the purity of impurities, which also are more or less dissolved Bayer alumina. by the acids. These are chiefly the oxides of It is known to disintegrate the previously heatchromium, vanadium, titanium and phosphorous. ed clay by means of watery sulphurous acid, with "'If special precautions are not taken, these subor without pressure. After removal of the silicic 10 stances are liable to be separated together with residue a clear aluminum sulphite solution is obthe alumina. Upon treatment of the alumina to tained. Certain difiiculty is encountered initially produce aluminum they then enter into the metal, in obtaining from this aluminum sulphite soluand render the latter, for many purposes, inferior. tion a raw alumina containing the smallest pos- In this manner, for example, by reason of these sible amount of $02, in order that the loss of substances, the electrical conductivity of the alualkali will be as small as possible when again minum is very greatly reduced. dissolving the alumina in the alkaline liquor.

According to the invention, an alumina sat- To obtain a raw alumina as poor as possible in .isfying all requirements with regard to purity sulphur, one of two methods may be adopted:

may be obtained from clay and similar silicious In the first place the aluminum sulphite solu- 20 minerals, such as China clay, leucite, etc., by distion may be decomposed by means of steam. If integrating these minerals in the known manner weak sulphite solutions and an excess of steam by calcination and treatment with watery sulare employed, a raw alumina is precipitated right phurous acid, separating the resulting clear soat the very commencement containing little sullution from the insoluble silicic acid, precipiphur. 25 tating a raw alumina from the clear solution, cal- The S-content may be further diminished by cining the raw alumina, dissolving the calcined, lengthy boiling of this solution. It has been raw alumina in the known fashion in alkaline found to be particularly suitable to allow the liquor, and treating the resulting solution, after precipitated raw alumina to settle, to remove the Separation of the impurities, to p oduce a pure upper solution, and then to boil the raw alumina hyd t of alu nah aw alu ina s pr ferwith a concentrated solution of salt. For this b y produced by decomposing the aluminum sulpurpose there may be employed, for example, a p t s u y heating d h pas f sodium chloride or calcium chloride solution. By Steam, so that ydrate is obtained, which is increasing the boiling point of the salt solution as poor as possible in sulphur. The sulphurous removal of the sulphurous acid from the deposit acid escaping may again be utilized in the process. is considerably accelerated. Finally, the slight s procedure s shown i the a mp y ng traces of sulphurous acid still remaining in the drawing which is a flow sheet of the process. raw alumina may be removed by caustic lime or I The precipitated raw alumina, in accordance soda or ammonia. The ammonia may be rewith th inv n, ay be il d for a cercovered from the solution in the known fashion tain length of time with a solution of common by distillation. The alumina is then dissolved salt in order to reduce the sulphur content. The in sodium lye or aluminate lye, in similar fashion residual sulphur compounds still remaining in the to bauxite in the Bayer process, and from the raw alumina may be conveniently removed by lye alumina produced in purest form in the known 45 alkaline means. In order to render any iron commanner. pounds in the raw aluminaharmless, the dissolv- Secondly, in place of the method just described, ing of the raw hydrate of alumina in the alkaline the procedure may also be such that the sulphite liquor is carried out with the admission of air, solution is decomposed in the known fashion at so that the iron compounds are oxidized. By temperatures between and The raw alumina, which in this case may contain a comparatively large amount of sulphurous acid, is filtered and calcined at a temperature of less than 900, and preferably of 450-550. In this connection it has been found that the presence of inert or reducing gases is particularly favorable, as oxidation of the sulphurous acid is then prevented and any sulphite which may have been formed is reduced.

A particular advantage of this process resides in the fact that an alumina. is obtained, which may be dissolved in sodium lye more readily than any other technical alumina known heretofore. The same may be dissolved without pressure in the lyes which are obtained upon stirring in the Bayer process, and the temperatures may be kept between 20 and 50". This has the advantage'that the aluminate lye does not require evaporation as otherwise necessary in the Bayer process, and moreover that the lye does not require to be raised to high temperatures, as otherwise essen-' tial in an autoclave.

Before the raw alumina is dissolved in alkaline liquors the small traces of sulphides remaining may be removed also in this case by alkaline means.

To facilitate comprehension of the invention two examples may be quoted as follows:

Per cent A1203 22 .62 S02 .5 1 F6203 .04 T102 .0 1

This raw alumina is then dissolved in the known fashion in aluminate lye according to the Bayer process at 20-60, in the manner usual in the case of bauxite.

From an aluminum sulphite solution of the following composition:

33.5 grammes A1203 and 250 grammes S02 per litre, with the following impurities (calculated on the basis of 100 parts A1203) Parts there was precipitated by hydrolysis a raw hydrate of alumina with 25.5% A1203 and 30.6% S02.

This contains for every 100 parts A1203 Parts The product was freed to a large extent of water and S02, a residue being obtained of the following composition:

Per cent A203 88.8 15

and in addition thereto the impurities of T102, Cr203 and V205, as in the original hydrate, and 20 a certain quantity of water.

If the product was calcined at 550 with the conduction of hydrogen gas, the following product Was obtained:

Per cent 25 A1203 90. 4

The calcination productwas dissolved in sodium lye, the impurities iron, titanium and chro 30 mium remaining behind in undissolved condition. After filtration there was obtained from the aluminate lye by mixing a pure hydrate of alumina. 35

What We claim as new and desire to secure by Letters Patent is:

1. Process for the manufacture of alumina which comprises disintegrating clay and similar minerals by calcination and treatment with an aqueous solution of sulfurous acid thereby pro-- ducing an aqueous solution containin aluminum sulfite, precipitating alumina. from said solution by heating, calcining the precipitated alumina, dissolving the calcined alumina in alkali lye and precipitating alumina from the resulting solution 45 by heating.

2. Process as defined in claim 1 in which alumina is precipitated from the solution containing aluminum sulfite by heating at from to C. and in which the so precipitated alumina is calcined at a temperature below 960 C.

3. Process as defined in claim 1 in which the precipitated alumina is calcined at from 450 C. to 550 C.

4. Process as defined in claim 1 in which the calcination of the precipitated alumina is carried out in a non-oxidizing atmosphere.

5. Process as defined in claim 1 in which the precipitated and calcined alumina is dissolved in dilute soda lye at a temperature of from 20 to 60 C.

6. Process as defined in claim 1 in which the calcined alumina is dissolved in a dilute aluminate lye.

7. Process as defined in claim 1 in which the alumina is calcined in a reducing atmosphere.

8. Process as defined in claim 1 in which the calcined alumina is dissolved in an alkali lye while introducing air into the lye.

WILHELM FULDA. ERICH WIEDBRAUCK. RUDOLF REINHARD BRUNO WITTIG. 

